The present invention relates to improvements in a clutch device of an automatic transmission, and more particularly to a rotation clutch device which varies an engagement capacity thereof.
Generally, an automatic transmission is set in a predetermined shift speed by selectively engaging a plurality of friction elements through fluid pressure. Many clutches of the friction elements are of a rotation clutch device which rotates in the automatic transmission. A publication "SERVICE MANUAL FOR FULL-RANGE AUTOMATIC TRANS-AXLE OF NISSAN RE4F02A TYPE" discloses a typical automatic transmission which includes a rotation clutch device such as a low clutch or high clutch. Each rotation clutch device of this typical automatic transmission is arranged such that an engagement capacity thereof is fixed. Some conventional automatic transmissions are arranged to engage a rotation clutch device in a plurality of shift speeds whose required torque share ratios are different from each other. Accordingly, the conventional rotation clutch device is designed so as to adapt to the shift speed whose required torque share ratio is maximum. This increases the size of the rotation clutch device so as to require a large space for this device and to increase a production cost thereof. In addition, when the shift change to a shift position whose required torque share ratio is small is executed, it is necessary to finely control the clutch operation pressure while keeping it at a small value in order to suppress a shift shock. Further, even if a source pressure of the clutch working pressure is fluctuated slightly, the clutch working pressure is largely affected to increase the fluctuation of the shift change performance of the automatic transmission in the above mentioned shift change. This degrades the quality of the automatic transmission. On the other hand, some non-rotation type clutches are of a variable engagement capacity type which has a plurality of piston chambers for varying the engagement capacity. However, if such structure of the non-rotation clutch is simply applied to a rotation clutch, the rotation clutch generates a dragging due to the rotation itself. In order to improve this dragging, a UD clutch of a rotation type installed in an automatic transmission of F4A42 (INVECS-II) type, which is produced by MITSUBISHI MOTORS CORP., is arranged to include a centrifugal pressure cancel chamber for canceling a centrifugal pressure generated in a clutch piston chamber.
However, if such multi piston chamber structure of the non-rotation type clutch is applied to the rotation clutch, it is necessary to provide a plurality of centrifugal pressure cancel chambers to cancel the centrifugal pressures of the plurality of piston chambers. This complicates the structure of the rotation clutch and increases a production cost thereof.